The little skate, Leucoraja, enters the LRT with Rhinobatos

Johanson et al. 2019 report:
“Evolutionary variation in anteroposterior patterning of the axial skeleton is a major contributor to the evolution of the vertebrate body plan, with five canonical vertebral types in tetrapods (cervical, thoracic, lumbar, sacral, caudal). However, less is known about the evolutionary origin and variation in vertebral regionalization patterns outside of tetrapods where described vertebral types range from as few as two in some chondrichthyans to eight or more in some teleost fishes. The synarcual is a specialized adaptation of the anterior axial skeleton comprising a putatively fused array of vertebral elements characteristic of jawed vertebrate (gnathostome) clades such as batoid and chimaeroid chondrichthyans where they support enlarged pectoral fins and dorsal fin spines respectively, as well as a fossil group known as the placoderms.”

Here,
the large reptile tree (LRT, 1996+ taxa) supports the hypothesis that the synarcual is indeed a fused series of ‘cervical’ vertebrae. In Jagorina + Manta, Torpedo, placoderms, hornbills, jerboas, porcupines, dolphins and mysticetes, a synarcual develops by convergence.

References
Johanson Z, Mertin K, Fraser G and James K 2019. The Synarcual of the Little Skate, Leucoraja erinacea: Novel Development Among the Vertebrates. Front. Ecol. Evol., 05 February 2019 | https://doi.org/10.3389/fevo.2019.00012
Malm AW 1877. Göteborg och Bohusläns fauna, Ryggradsdjvren.
Mitchell SL 1825. The hedgehog-ray – a species of Fish taken occasionally near New-York, in the Atlantic Ocean, and now, as is believed, for the first time described American Journal of Science and Arts, 9: 290.
Vanburen CS and Evans DC 2016. Evolution and function of anterior cervical vertebral fusion in tetrapods. Biological reviews of the Cambridge Philosophical Society 92(1).